This invention relates in general to power take-off units for selectively providing rotational energy from a source of rotational energy to a driven accessory. In particular, this invention relates to an improved structure for a power take-off unit that includes an attached pneumatic valve.
A power take-off unit is a well known mechanical device that is often used in conjunction with a source of rotational energy, such as a vehicle engine or transmission, to provide rotational energy to a driven accessory. For example, power take-off units are commonly used in industrial and agricultural vehicles to provide rotational energy to hydraulic pumps that, in turn, are used to operate hydraulically driven accessories such as plows, trash compactors, lifting mechanisms, winches, and the like. The power take-off unit provides a simple, inexpensive, and convenient means for supplying energy from the source of rotational energy to the hydraulic pump that, in turn, provides relatively high pressure fluid to operate the driven accessory.
A typical power take-off unit includes an input mechanism and an output mechanism. The input mechanism of the power take-off unit is adapted to be connected to the source of rotational energy so as to be rotatably driven whenever the source of rotational energy is operated. The output mechanism of the power take-off unit is adapted to be connected to driven equipment, such as the hydraulic pump, or any other device that requires rotational torque and speed. In some instances, the input mechanism of the power take-off unit is selectively connected to the output mechanism, for example via an input cluster gear meshed with the output gear, such that the hydraulic pump is rotatably driven whenever the source of rotational energy is operated. In other instances, a clutch assembly is provided between the input mechanism and the output mechanism such that the hydraulic pump is selectively driven only when the source of rotational energy is operated and the clutch assembly is engaged.
A typical hydraulic pump includes a fluid inlet port, a fluid outlet port, and a pumping mechanism. The fluid inlet port is adapted to communicate with a reservoir containing a quantity of relatively low pressure hydraulic fluid, while the fluid outlet port is adapted to communicate with the hydraulically driven device. The pumping mechanism of the hydraulic pump is adapted to be connected to the output mechanism of the power take-off unit so as to be rotatably driven whenever the power take-off unit is operated. Thus, when the power take-off unit is operated, the hydraulic pump draws relatively low pressure hydraulic fluid from the reservoir and supplies a flow of relatively high pressure hydraulic fluid to the hydraulically driven device.
The components of the power take-off unit are typically supported within a housing that is closed to retain lubricant and to prevent the entry of dirt, water, and other contaminants therein. In many instances, the power take-off unit housing is formed from first and second power take-off unit housing portions that are separate from one another, but are secured together to form a sealed enclosure for the components of the power take-off unit. For example, the first power take-off unit housing portion may be generally hollow in shape, having an opened end and a closed end, while the second power take-off unit housing portion may be generally flat and circular. The second power take-off unit housing portion can be secured to the first power take-off unit housing portion so as to close the opened end thereof and thereby form the power take-off unit housing. Such a two-piece structure facilitates the assembly and servicing of the components of the power take-off unit, and further allows either or both of the input and output mechanisms of the power take-off unit to be rotatably supported on the closed end of the first power take-off unit housing portion and the second power take-off unit housing portion.
In many instances, the power take-off unit further includes a clutch assembly for selectively disconnecting the output shaft from the input gear. The use of a clutch assembly in a power take-off unit is desirable because it permits selective or intermittent operation of the driven accessory without having to park the vehicle and stop the transmission gears from spinning. When the clutch assembly is engaged, the output shaft is rotatably driven by the input gear. Consequently, the driven device is operated by the vehicle engine. Conversely, when the clutch assembly is disengaged, the output shaft is not rotatably driven by the input gear. As a result, the driven device is not operated by the vehicle engine.
Typically, the clutch assembly is engaged by pressurized fluid from a transmission oil pump. Alternatively, in a truck having a transmission that does not include an attached oil pump for example, a source of pressurized air may be provided from a truck's air brakes through a pneumatic valve located remotely from the power take-off unit at a location near the source of pressurized air or between the air brakes and the power take-off unit.
Although the installation and assembly of the pneumatic valve and associated pneumatic lines in a vehicle in this manner has been satisfactory, the need has arisen to reduce the overall number and size of parts required to deliver pressurized air to the clutch assembly in a power take-off unit. Thus, it would be desirable to provide an improved structure for a power take-off unit that includes a pneumatic valve having a reduced size and number of parts, and is attached to the power take-off unit.